A. Field of the Invention
This invention pertains to the field of membrane-type filter devices, particularly intravenous filter devices which employ both hydrophilic and hydrophobic membranes.
B. Description of Related Art
This invention relates broadly to membrane-type filter devices, and especially to filter devices used to remove impurities from liquids or fluids that are to be introduced intravenously to the human body. Some fluids useful with this invention include blood, plasma, glucose solutions and drugs. Other fluids useful with this invention are not listed but are well known to those having ordinary skill in the art.
One of the problems encountered with conventional membrane-type intravenous filter devices is the presence of gas. The fluid must be filtered before entering the patient in order to remove gas bubbles and contaminants. Gas in the housing or mixed with the liquid tends to prevent effective filtration of the liquid. When the filter is first attached to the patient and fluid flow is initiated, air frequently enters the lines or is already present in the filter device. This air tends to prevent the liquid from wetting a hydrophilic membrane which filters the liquid. A non-wetted hydrophilic membrane filter will generally not allow the liquid to pass. Thus, entrapped air tends to prevent fluid from entering the patient. It is therefore desirable to remove this entrapped air as quickly and continuously as possible.
Several devices are available to remove air from membrane-type filter devices. These devices make use of hydrophobic membranes which are capable of passing air but not liquids. Conventional intravenous filters employ this principle but have some shortcomings. For example, several commercial devices are not altogether satisfactory because they do not remove air through the outlet in the short time that is necessary. Some provide single vents; in these, air is sometimes entrapped in areas of the housing that are not contiguous to the hydrophobic membrane, especially when the orientation of the filter device makes it such that air cannot contact the hydrophobic membrane.
Various devices have attempted to correct these shortcomings. Some utilize rectangular filters to assist self-priming, with an inlet at the bottom and an outlet at the top of the filter. Such devices must be tilted from a horizontal plane in order to be self-priming. Some do not utilize a hydrophobic-type filter medium. Still other filter units employ a combination of hydrophilic and hydrophobic filters arranged side-by-side in alternate sequence. A disadvantage, however, is that this single plane configuration provides a hydrophobic zone on each end of the housing. Although these chambers appear to provide for the escape of entrapped air, they also create a zone where liquids can gather and be incapable of passing through either the hydrophilic membrane or the hydrophobic membrane. Further, drugs in intravenous fluids often have different densities than other fluids administered to the patient. When this is the case, the drugs may stratify and gather at these zones. Accordingly, if the filter unit is in a vertical position, the liquids will not immediately be administered to the patient. This could conceivably cause problems, especially if drugs must be administered quickly to the patient.
The problems enumerated in the foregoing are not intended to be exhaustive but rather are among many which tend to impair the effectiveness of previously known filter devices. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that filter devices appearing in the art are not altogether satisfactory.